I have a power supply with a different connector, and output (on one of 24 pins) to the circuit input I am attempting to use it with, so basically I got an electronics engineer I know to make an adapter up for me, he did a great job in doing so however I have one issue, one of the pins of this adapter's input side is of 5V DC but I need it to be 12V DC on the output, the engineer used a simple 0-240V to 12V transformer however this doesn't appear to be working.

What is the best way to achieve this 5V DC to 12V DC conversion? Thank you in advance.

A 12V transformer produces a peak voltage of (12V x the root of 2=) 17V. A bridge rectifier reduces it to 15V at a high current or a little more at a low current. A filter capacitor charges quickly to 15VDC and can feed a 12V regulator.

I have a power supply with a different connector, and output (on one of 24 pins) to the circuit input I am attempting to use it with, so basically I got an electronics engineer I know to make an adapter up for me, he did a great job in doing so however I have one issue, one of the pins of this adapter's input side is of 5V DC but I need it to be 12V DC on the output, the engineer used a simple 0-240V to 12V transformer however this doesn't appear to be working.

What is the best way to achieve this 5V DC to 12V DC conversion? Thank you in advance.